In applications related to circuits, reference voltage generators are frequently used to generate reference voltages for other circuits to use. A reference voltage generated by a conventional reference voltage generator may be a fixed voltage which is substantially invariant with temperature. When a reference voltage generator is applied with a high performance semiconductor circuit, the semiconductor circuit may generate a bias voltage according to a reference voltage provided by the reference voltage generator. It is better for the bias voltage to be variant with different temperature conditions for better circuit performance. Therefore, how to make a reference voltage generator provide a reference voltage varying with temperature has been a problem to be solved in the field.